Ptyctimous Mites (Acari, Oribatida) of Peru with the Description of an Extraordinary New Phthiracaroid Mite from the Peruvian Andes

Simple Summary In this work, a new species of ptyctimous mite (“box mite”)—Protophthiracarus afthonos—is described and illustrated. It is exceptional by its very rich body setation—bigger than in any other known member of the ptyctimous oribatids. The new species was found in a forest soil sample from the Andes in Peru. The discovery confirms the uniqueness of the montane arthropod fauna of South America. The biogeographic distribution of ptyctimous oribatids in Peru is summarized and supplied with a key to the species of Peruvian fauna. Abstract Protophthiracarus afthonos sp. nov. is described and illustrated using line drawings, transmitted light and SEM imaging. It is characterized by an extraordinary richness of notogastral setae (ca. 166 pairs) that has been previously unseen among phthiracaroid mites. The species originates from the material collected from the litter of primary forest in the Peruvian Andes. The genus Protophthiracarus is well represented in the Neotropical Region. Many species of ptyctimous mites have been found in Peru, representing both widespread and endemic biogeographic elements. Among a total of 37 species, 20 from Peru have been described for the first time. Currently, the ptyctimous fauna consists of 12 endemite, 11 neotropical, 4 semicosmopolitan and 9 pantropical biogeographic elements.


Introduction
Ptyctimous mites (Acari: Oribatida) are doubtlessly one of the best-known taxonomic groups of oribatid mites worldwide. Despite so many new species being described from all geographic regions of the world, new habitats are being explored, yielding yet more new taxa.
Peru is covered by a diverse range of habitats, from the Amazon rainforest in the east, to the high Andes mountains in the west. These habitats support a remarkable array of plant and animal life, including mites. Currently, there are three land domains of faunas: Amazon (with Amazon, Yungas, Pacific, Equatorial and Páramo provinces), Chaco and Andean-Patagonian (with Puno, Deserts and Mountain Steppes provinces). Knowledge of the distribution of most of invertebrate groups among those biogeographic units is fragmentary at best, if not nonexistent.
Peru is occupied by various vegetation units, namely mixed zones with evergreen wet tropical forests, mountainous tropical and subtropical wet forests, dry equatorial climate forests, savannahs and semideserts, trees and shrubs, grasslands, cushionplants and shrubs, and moss and lichens [1].
Legs (Figures 2H,4E,F and 5). Chaetome complete. Setae d, l and v slightly remote from the anterior end of its segment and situated almost at the same level; seta v situated posteriorly. Etymology. The specific epithet is derived from Greek afthonos meaning "abundant" and refers to the polytrichy of the notogastral setae.
Comparison and diagnosis. This species is distinguishable by the huge neotrichy of the notogastral setae. Multiplication of a number of setae applies to all rows on notogaster, namely: c, d, e, h and ps. In other species revealing notogastral neotrichy, the enlarged number (multiplication) of setae applies typically to the setae of rear notogastral rows, usually h and ps. extremely difficult to distinguish the setae of appropriate rows. Vestigial setae invisible. Three pairs of lyrifissures (Figure 3), ia, im and ip present.
Legs (Figures 2H,4E,F and 5). Chaetome complete. Setae d, l″ and v′ slightly remote from the anterior end of its segment and situated almost at the same level; seta v″ situated posteriorly.
Etymology. The specific epithet is derived from Greek afthonos meaning "abundant" and refers to the polytrichy of the notogastral setae.
Comparison and diagnosis. This species is distinguishable by the huge neotrichy of the notogastral setae. Multiplication of a number of setae applies to all rows on notogaster, namely: c, d, e, h and ps. In other species revealing notogastral neotrichy, the enlarged number (multiplication) of setae applies typically to the setae of rear notogastral rows, usually h and ps.

A systematic list of ptyctimous mite species (Oribatida) of Peru
Synonymes are only supplied for species included in the literature cited in this paper; for a complete list of the synonymies of species recorded in Peru, see Niedbała 1992 and2004. Species names are supplied with a biogeographic element epithet. Species described from Peru as new are marked with asterisk (*). Spellings and collocations of taxonomic names follow the recent catalogue by Niedbała and Liu [6].

List of localities and species of ptyctimous Oribatida found in Peru.
The list contains standardized data, with corrections of apparent mistakes in primary sources, modern transliterations of geographic names and the numbers of collected individuals of each species recorded. In addition, it follows the original format as much as possible. Biogeographic distribution is depicted in Figure 6, with locations marked by numbers in braces below.

Discussion
The phenomenon of setal multiplication on the particular body area of mites is known under the name neotrichy: "Néotrichie est la terme générale [. . .] est la formation secondaire de poils, dans un territoire, par la multiplication de poils préexistant dans ce territoire" [27,28]. Neotrichy is well known among phthiracaroid mites, where extra setae appear usually on the notogaster and anoadanal plates. It also sometimes results in hyper-trichy, as exemplified by P. afthonos n. sp.
We report a new species of the genus Protophthiracarus (Phthiracaroidea) from the Peruvian Andes, which has a high, previously unseen number of notogastral setae. To our best knowledge, this is the second case of such rich neotrichy of notogastral setae ever known. Until now, the most hairy ptyctimous mite species known and probably the most neotrichous oribatid mite ever was Atropacarus (A.) niedbalai from New Zealand [29]. This species shows extreme neotrichy on the prodorsum, notogaster, genitoaggenital and anoadanal plates, whereas the neotrichy of the newly described Protophthiracarus afthonos is seen on the notogaster and anoadanal plates only. However, the number of setae on the notogaster being ca. 166 pairs is fairly higher than that of the New Zealand species (109-115 pairs). The neotrichy on the notogaster has a form of plethotrichy because numerous setae are displaced unevenly and asymmetrically arranged.
Neotrichy occurs independently in different phylogenetic linages of phthiracaroid mites [5] and, in the case reported herewith, concerns the taxon belonging to the genus Protophthiracarus, which is generally poor in species. It is more frequent in species from the Southern Hemisphere, especially Neotropical and Australasian regions [27][28][29][30].
It is also worth mentioning that the neotrichy itself cannot be considered an argument strong enough to create upper-level taxa [5,27,30].
The genus Protophthiracarus was proposed by Balogh [31], with a type species Notophthiracarus chilensis Balogh et Mahunka, 1967 [32]. It is well represented in the fauna of the southern hemisphere, except the Australasian region. The genus Protophthiracarus comprises 47 described species and 2/3 of them originate from the Neotropical region.
All species reveal similar proportions in biogeographic distribution, those being endemites (11 species), neotropical (11 species) and widely distributed ones (semicosmopolitan-4 species, and pantropical-9 species), each group sharing ca. 1/3rd of the pool [6]. Endemic species are generally scarce, possibly except for Mesoplophora (Mesoplophora) quasigaveae. Two endemic species are numerously represented in few samples, but each from one region only: A. excellens at Machu Picchu, and M. quasigavae in the Puerto Inca Province.
The majority of more broadly distributed species occur in a larger number of various localities, e.g., pantropical A. vestita in 17, neotropical M. curviseta in 20 and A. peruensis in 10 localities. The number of individuals is not distribution-dependent, and even though the most numerous are neotropical species, pantropical and endemic species are also numerous, and two pantropical and endemic species are richest in numbers.
Three neotropical species, A. clavata, N. fornicarius and N. inauditus, reveal that Guyanan distribution occurs only in the northern part of the Neotropical region (Antilles, Venezuela, Ecuador, Peru, Bolivia). This may prove that quite specific climatic and environmental factors shape the distribution of ptyctimous mites in Peru.
The reported resulting individual counts were collected from a variety of substrates, ranging from soil and litter through to decayed organic plant matter and to lower vascular and epiphytic plants.
Most of the geographic localities from where the mite material is reported herewith are within the Andes range and its highland vicinities. This apparently reflects more the attitude of the collectors than the true geographic distribution of the species. Thus, our conclusion is that ptyctimous Oribatida needs more extensive sampling from mountain and highland (and to some extend lowland tropical) areas in order to evaluate its real abundance and density.